#include <stdio.h>
#include <string.h>

int n;

void fact(int nums[n], int index)
{

    int sum = 0 , len = n;

    for (size_t i = 0; i < len; i++)
    {
        for (size_t k = i+1; k < len; k++)
        {
            sum=nums[i]+nums[k];

            //检查是否有重复
            for (size_t z = 0; z < len; z++)
            {
                if(sum==nums[z]){
                    printf("Case #%d: It is not a B2-Sequence.\n\n", index);
                    return;
                }
            }
           
        }
        
    }
    printf("Case #%d: It is a B2-Sequence.\n\n", index);
    
}

int main(int argc, char *argv[])
{

    int index = 0;

    while (scanf("%d", &n)!=EOF)
    {
        int nums[n];
        memset(nums, 0, n);

        for (size_t i = 0; i < n; i++) //控制输入数字
        {
            scanf("%d", &nums[i]);
        }
        fact(nums,++index);
    }

    return 0;
}
